The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.
When trauma or disease causes the lens to become less transparent, vision deteriorates due to the diminished light that is transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
One accepted method for treating cataractous lenses is to remove the lens by a surgical technique called phacoemulsification. During this procedure, an opening is made in the anterior capsule and a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by the IOL.
The IOL is generally implanted using an insertion apparatus or device, such as an intraocular injection cartridge, that rolls, folds, or otherwise configures the lens for delivery through the small opening in the eye in a way that reduces trauma and expedites post-surgery healing. Injectors for delivering IOLs typically employ a handpiece and a cartridge having a hollow insertion tube or cannula through which the folded IOL is passed using a pushrod. The cartridges may be made of disposable materials, such as plastics, and remain in a sterile package until ready for coupling with the handpiece. Some injectors operate without the cartridge and are reusable. The IOL may be stored separately and transferred to a load chamber in the injector or cartridge just prior to delivery. Typically, the load chamber is first partially filled with a liquid or gel, for example, a viscoelastic medium or ophthalmic viscosurgical device (OVD). The lubricating viscoelastic facilitates passage of the IOL through the injector. The viscoelastic substances may be preloaded in a syringe, typically having a thin cannula tip through which the viscoelastic is delivered to the load chamber in the IOL injector.
The IOL is placed in the IOL injector in a folded state. The IOL is injected into the eye through the same small incision used to remove the diseased lens. The tip of the IOL injector is inserted into the incision, and the lens is delivered into the eye.
IOLs may be manufactured from a variety of materials, and include polymers that exhibit specific characteristics. These characteristics allow the lens to be folded, and when delivered into the eye, allow the lens to unfold into the proper shape. The polymers used to make these lenses have characteristics that tend to be temperature dependant. Heating the polymer allows the IOL to be compressed and folded more easily, thus allowing it to fit through a smaller incision. A smaller incision is desirable because it promotes faster healing and is less traumatic for the patient.
The temperature characteristics of the polymers used to make IOLs may have a significant impact on the lens implantation process. For some polymers, a change in hardness or viscosity occurs over a relatively narrow temperature range. For example, at colder temperatures, the polymer may become brittle and break if folded. At higher temperatures, the polymer may become gummy and lose its shape retaining ability. Therefore, it may be advantageous to maintain the polymer in a specific temperature range to enable the IOL to maintain its physical integrity.
In practice, some surgeons have resorted to manually heating IOLs, for example, using the outside of autoclaves or warmers designed to warm baby wipes. Such warming, however, is uncontrolled and unlikely to warm the IOL to an optimum temperature. As previously noted, the polymers used to manufacture artificial lenses are sensitive to temperature, and more precise temperature control may help achieve desired results.